The present invention relates to a structure for cooling an integrated circuit (IC) and, more particularly, to a structure for cooling an IC by transferring heat generated by the IC to a cooling fluid being circulated.
Cooling structures for the above application commonly include a heat conductor intervening between an IC and a cooling fluid or coolant. The heat conductor contacts the IC either directly or via a member having high thermal conductivity. Heat generated by the IC is transferred to the coolant via the heat conductor and then entrained by the coolant to the outside. With this kind of structure, it is possible to increase cooling efficiency by reducing heat resistance between the IC and the coolant. The heat resistance can be reduced if the heat conductor and IC are held in close contact over a broad area.
However, the close contact of the heat conductor and IC is susceptible to the irregularity in the height of the IC and the inclination of the IC. Specifically, when the height of the IC is short, a gap is left between the IC and the heat conductor. Further, when the upper surface of the IC is inclined, the heat conductor contacts only a part of the upper surface of the IC. Let the irregularity in the height of the IC and the inclination of the IC be referred to as factors obstructing contact. Such factors obstructing contact are particularly problematic when a plurality of heat conductors contact a plurality of ICs. In such a case, the heat conductors have to be adjusted in height and inclination one by one in matching relation to the heights and inclinations of the associated ICs.
An IC cooling structure elaborated to eliminate the factors obstructing contact and insure the close contact of the heat conductor and IC is taught in, for example, U.S. Pat. No. 5,023,695. This U.S. Patent shows in FIG. 1 thereof a conventional cooling structure having an IC 101 mounted on a printed circuit board 102, a piston 104 having a spherical portion contacting the IC 101, a hat or cooling plate 106 accommodating the piston 104, a spring 105 urging the piston 104 against the IC 101, and a coolant 109. The piston 104 and hat 106 constitute a heat conductor in combination. Heat generated by the IC 101 is transferred to the coolant 109 via the piston 104 and hat 106. Since the spring 105 constantly urges the piston 104 against the IC 101, the piston 104 remains in contact with the IC 101 with no regard to the height of the IC 101. Further, since the tip of the piston 104 is spherical, the piston 104 and IC 101 contact each other over a substantially constant area with no regard to the inclination of the IC 101.
The above U.S. Patent shows another conventional cooling structure in FIG. 2 thereof. In the structure of FIG. 2, a chip 201 is mounted on a printed circuit board 202 while a heat-conducting substrate 203 is provided on the chip 201. An elastic heat-conducting material 204 is provided on the substrate 203. A heat-conducting plate 205 is positioned on the heat-conducting material 204 and retained by a thin flexible bellows 207 made of metal. Heat generated by the chip 201 is transferred to the coolant via the substrate 203, elastic material 204, and plate 205. The plate 205 implements the heat conductor. The bellows 207 is flexible in the up-and-down direction and maintains the plate 205 in contact with the elastic material 204 with no regard to the height of the chip 201. In addition, the plate 205 inclines in association with the inclination of the chip 201. Hence, the entire surface of the plate 205 and the elastic material 204 contact each other even when the chip 201 is inclined.
However, the conventional structures shown in FIGS. 1 and 2 of the above U.S. Patent have the following problems. In the structure of FIG. 1, the heat conductor is constituted by two independent members, i.e., piston 104 and hat 106. Helium gas 100 fills a gap between the piston 104 and the hat 106 to effect heat transfer. However, since the heat transfer coefficient of the Helium gas 100 is smaller than the heat transfer coefficient of the piston 104 and that of the hat 106, the heat resistance of the heat conductor is high. Moreover, in this conventional structure, the contact of the IC 101 and piston 104 is implemented by a spherical surface, so that the contact area is small. Consequently, the heat resistance between the IC 101 and the piston 104 is increased.
The structure of FIG. 2 includes the thin bellows 207 made of metal. It is likely that such a bellows 207 corrodes when use is made of water or similar coolant. When a hole is formed in the bellows 207 due to corrosion, the coolant will flow out therethrough and cause electronic parts arranged on a circuit board 202 to fail.